I think I have found a workaround to my own issue.

Open WLAN connection manager
Don't create (or delete existing) preferred networks
select the available network
connect
When it asks for it to be added to the preferred network, say no!
Connection then proceeds OK
This seems to prevent the WLAN tool from hanging, and it can then be closed leaving a reliable link.
I hope this helps some others with their issues.
Obviously it means I will have to re-enter my WPA password whenever I boot up or need to re-connect, but that's not very often for me.